1. Field of the Invention
Embodiments of the present invention relates to methods for fabricating metal nano-particle embedded enhancement substrates used for surface enhanced Raman spectroscopy (SERS) and surfaces for SERS.
More particularly, the present invention relates to methods for fabricating metal nano-particle embedded enhancement substrates used for surface enhanced Raman spectroscopy (SERS) and surfaces for SERS, where the methods include ion implanting an initial substrate (matrix) with metal ions up to a dose and at a beam current density sufficient to form metal nano-particles in the matrix with or without subsequent thermal annealing and optionally etching of the implanted surface to partially expose the metal nano-particles to form a SERS substrate.
2. Description of the Related Art
Surface enhanced Raman spectroscopy (SERS) is used for detection and identification of molecules present in minute quantities. The molecule being detected is adsorbed on a substrate consisting of nano-sized metal features, which is known to enhance the Raman scattering signal from the adsorbed molecule by many orders of magnitude. The large signal enhancement facilitates the detection of molecules present in very small quantities and the high sensitivity is beneficial in detection of chemicals in trace quantities, in bio medical applications, for example, in detection of pathogens or identification of tissue anomalies indicative of medical conditions.
To date, methods for preparation of SERS substrates have shortcomings with reproducibility of SERS detection. Advanced nano-structured substrates that render reproducible results require complex fabrication techniques having many fabrication steps thereby have a high production cost. Further, such substrates have a limited shelf life. The existing fabrication techniques have less flexibility with regard to the choice of initial substrate (matrix) and the geometry of the matrix. For example, a fabrication method that is applicable on a plane, wafer-shaped starting substrate may not be equally applicable to a probe shaped initial substrate, such as the surface of an optical fiber. Existing fabrication techniques that yield high performance may not be applicable to different materials that make up the initial substrate. For example, a method used for nano-structure fabrication on silicon may not be suited for fabrication on glass.
Since the discovery of surface enhanced Raman spectroscopy (SERS), there have been many reported methods for fabrication of substrates that show SERS effect. Certain methods of fabricating SERS substrates rely on making metallic structures with sizes and separations far less than the wavelength of excitation light source to induce high electromagnetic field enhancements. Some of the present techniques include directed pattering approach using nano-sphere lithography and E-beam lithography where patterns are produced on a substrate, typically using Ag or Au. Ag has been found to be the best material for surface enhancement. The challenge in these techniques is to reduce the distance between features due to the limitations of the lithographic techniques. Another approach utilizes random features arising, for example, from electro deposition and sputter coating. However, due to the limitations of the inherent process parameters, the controllability and reproducibility of these techniques are poor. Here, we show a technique where high dose Ag ion implantation into silicon is utilized to produce an Ag nano particle-Si composite, which is an effective, stable and reproducible SERS substrate.
Thus, there is a need in the art for SERS substrate manufacturing technique that addresses the problems with prior art manufacturing techniques, where high dose metal ion implantation into substrate is utilized to produce a metal nano-particle/substrate composite, which is an effective, stable, and reproducible SERS substrate.